As well known, hydrogen can reduce the strength of the metal workpieces with which it comes systematically into contact. This is true, in particular, in the case of steels. In fact, a long-lasting contact with hydrogen gas, as it may be the case in some process environments, may cause hydrogen to be absorbed into the metal. Beyond a certain extent, this may give rise to hydrogen embrittlement. For instance, chemical or electrochemical surface treatment processes are known for treating metal workpieces, such as galvanic treatments, pickling, chemical milling or electropolishing. These processes take place by a reduction reaction of the hydrogen that is present as H+ ion in a treatment bath. This way, atomic hydrogen is generated that may remain within the treated workpiece, and may cause embrittlement.
Various procedures are known for assessing the risk of hydrogen embrittlement in an industrial galvanic treatment process. For instance, ASTM F519-10 provides destructive tests on a significant number of specimens that must be prepared according to specific procedures. ASTM F 326-96 provides measuring a hydrogen absorption parameter during the treatment, and measuring its permeability during a subsequent dehydrogenation treatment. These procedures have the drawback of being too costly. Moreover, these are indirect and not well-timed tests. In other words, samples are used that are distinct from the workpieces actually treated, and a certain amount of time must be waited in order for the results of the tests to be available. Therefore, if a result is not acceptable, it may be necessary to call back workpieces that have already been dispatched or that are even already in use, which causes important loss of money, along with other disadvantages. Moreover, the above-mentioned procedures do not allow real-time adjustments of the process variable, in order to limit hydrogen absorption into the workpieces during the treatment, nor do they improve process efficiency.
The same also applies for treatments in which the surface of a metal workpiece is treated with an acid solution in order to remove an oxide surface layer. For example, pickling normally occurs by hydrogen production, which may cause hydrogen embrittlement. Moreover, the acid solution may be aggressive for the metal.
Therefore, a device is needed by which hydrogen absorption can be continuously followed in a galvanic treatment, or in treatments like pickling, such that real time data are available and, preferably, by which a process control can be carried out in order to prevent hydrogen embrittlement.
It is also known that the enamelling processes of metal workpieces may result into hydrogen absorption and surface embrittlement of the treated workpieces. In fact, when preparing the enamel frit, temperatures are normally achieved between 800° C. and 850° C. In these conditions, some water present in the enamel mixture is catalytically dissociated by the iron of the steel of the metal workpiece, therefore hydrogen is formed that is absorbed into the workpiece and then diffuses through the workpiece. In the subsequent cooling of the workpiece, hydrogen tends to migrate back to the surface of the workpiece, where it encounters an impervious enamel layer. The pressure of hydrogen may deteriorate and weaken this layer. This is the so called “fish scale” defect.
Therefore, a device is needed for preliminary permeation tests, in order to assess whether a metal workpiece can be enamelled without causing such behaviour.
The device traditionally used for preliminary permeation tests is the Devanathan-Stachurski cell, which comprises a hydrogen generation half-cell and a measurement half-cell. The cell allows measuring hydrogen diffusivity in a metal. This device is complicated since there are two half-cells that must be mounted together, since a tight connection must be ensured and for further minor reasons. Moreover, the tests have a considerable duration. Therefore, a device is needed for carrying out hydrogen permeation preliminary tests or for measuring hydrogen diffusivity through a metal material, which is more user-friendly and more reliable than the prior art devices.
In order to measure the content of hydrogen within metal workpieces, devices known as desorbers are used, which comprise an oven in which a sample, is arranged after enclosed within a quartz tube. The sample is then heated in order to cause absorbed hydrogen to come out of it, and to leave the oven in a gas stream. The hydrogen concentration in the stream is monitored, integrated and compared with the weight of the sample, thus obtaining a quantitative measure of the hydrogen contained in the sample. The desorbers are rather cumbersome and expensive, and also involve considerable operation and maintenance costs. Moreover, they only allow destructive tests. Therefore, a device is needed for determining the content of hydrogen incorporated in a metal workpiece that is less expensive, that involves lower operation and maintenance costs, and that is more user-friendly than conventional desorbers. Such a device is also needed for performing nondestructive tests.
It is also known that at least one step of the corrosion processes in a metal material occurs by producing hydrogen. This hydrogen production depends upon the corrosion intensity. Devices are also known for monitoring the flow of hydrogen as an indicator of corrosion events. These devices comprise amperometric sensors, so they do not provide a satisfactory reliability and strength.
As is well known, hydrogen is more and more used as an energy vector/fuel, for example, for powering motor vehicles. In particular, hydrogen gas distribution facilities and networks are developed comprising self-service pumps. For safety of such installations, devices are required for real time checking whether hydrogen embrittlement can occur in the metal of the ducts and of the gas bottles used for conveying and storing hydrogen gas. Nowadays, no device is known that can reliably detect and notify this hydrogen embrittlement risks.
US2009/0277249A1 describes a method and a device for determining the quality of a seal element by bringing a hydrogen-containing mixture into contact with the seal element and by measuring the amount of hydrogen that passes through the seal element, in the form of molecular hydrogen. The use is also mentioned of the same technique for carrying out permeation tests in a component, wherein hydrogen passes through the component, still in the molecular form. The technique does not allow determining the content of hydrogen that is present in the seal element, and does not allow determining hydrogen diffusivity through the seal element. Therefore, US2009/0277249A1 cannot assess the risk of embrittlement of the seal element, but the tightness degree of the seal element, i.e. how much hydrogen is lost through the seal element.
In EP1114992A2 a cap-shaped collection element is used that is provided with spiral-shaped ribs for collecting hydrogen coming from a surface of a workpiece, and an amperometric sensor is also used.
WO2011/131897A1 describes a process for monitoring the corrosion rate in a metal duct that conveys a corrosive fluid, in which a device is provided that is arranged to form, when the device is installed on a wall of the metal duct, a chamber configured for receiving hydrogen gas that permeates through the wall of the duct. The process comprises a treatment step for eliminating a metal species from the chamber, a step of measuring an amount of hydrogen that is received in the chamber, in order to estimate the corrosion rate of the duct metal. Even in this case, the measurement of permeated hydrogen is a permeability measurement, which increases due to the corrosion, but it cannot lead to the content of hydrogen that is present in the walls of the duct, nor can hydrogen diffusivity in the walls be determined.